discasaurus for $0 on ios. the course directory is large and pre-loaded pars (which can be changed on the fly) are accurate. zero frills but works great when all you want to do is keep score. I really like that it switches from score input mode to scorecard display mode just by rotating the phone from vertical to horizontal.

Why: You can search and upload courses straight from here (DGCR).
You can see your average for each course, and each hole.
You can see a line graph of your scores for each course.
You can see line graphs and pie charts of your scores for each hole.
You can easily send the scores to other people if you are keeping score for multiple people.

It's pretty great. I have never tried any others becuase I have no reason to, DC2 has everything. I think the paid version was like $3 - totally worth it.